Probing $ttγ$ and $ttZ$ couplings at the LHeC

We study the deep inelastic scattering and photo-production modes of $t\overline{t}$ pairs at the proposed LHeC and its potential to probe the electromagnetic and weak dipole moments (MDM and EDM for $ttγ$) of the top quark. A framework of eight independent gauge-invariant dimension-six operators involving the top quark and the electroweak gauge bosons is used. Four of these operators modify the charged $tbW$ coupling which can be probed through the single (anti) top production mode as reported in the literature. One generates $ttγ(Z)$ as well as $tbW$ couplings, while the other two do not generate $tbW$ but only $ttγ(Z)$. Our focus is on the MDM and EDM of the top quark for which the photo-production mode of $t\overline{t}$ can be an excellent probe. At the proposed electron energies of $E_e =60$ and $140$ GeV the LHeC could set constraints stronger than the indirect limits from $b\to s γ$ and the potential limits of the LHC through $t\overline{t} γ$ production.

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